The present invention relates generally to operations performed and equipment utilized in conjunction with a subterranean well and, in an embodiment described herein, more particularly provides a shear activated safety valve system.
In offshore well testing operations, it is common practice to use two safety valves connected to each other via a shear joint and ramlock sub. The shear joint is typically positioned in the shear rams, and the ramlock sub is typically positioned in the sealing rams of a subsea wellhead. The sealing rams seal about the ramlock sub.
In the event of an emergency, the shear rams can shear the shear joint, allowing an upper portion of the test string to be quickly retrieved either before or after the emergency has passed, and leaving a lower portion of the test string in the well below the wellhead. The lower safety valve prevents fluid from escaping from the well via the lower portion of the test string.
In the past, the safety valves have been generally operated using a control line or umbilical extending to a platform or rig at the surface of the water. It will be appreciated by those skilled in the art that it is quite expensive and time-consuming to install and pressure test this control line.
Safety valves have been developed which use a highly pressurized nitrogen chamber to produce a biasing force in an actuator of the valve. However, it will be appreciated that safety concerns need to be addressed when charging and handling such highly pressurized chambers at the surface.
Therefore, it may be seen that improvements are needed in the art of safety valve systems. The present invention provides such improvements. These improvements are not necessarily limited to the issues raised by the foregoing background information.